Yeti, just because you can see something doesn't mean it's not an optical illusion. Our eyes were designed primary to see colors and shapes; they are horrible judges of perception, depth, and distance. What you describe is just your eyes reaching the limit of depth perception and not being able to relay a coherent picture back to your brain.
There are dozens of videos out there showing that a boat appears to disappear, but then using a zoom camera like the Nikon P900 / P1000 you just zoom in a bit and it returns to ful view. That camera is one of the biggest reasons for the resurgence of Flat Earth. There was a movement in the late 19th century as well ... many books written on the subject.
There are so many videos demonstarting that we can "see too far" ... but one could argue they were faked ... except there are photographs taken by disinterested third parties who aren't Flat Earthers per se, such as this one.
https://www.facebook.com/watch/?v=554945265254988One of these days, I'll go out and try it myself.
Really the only comeback is a magical "refraction" which bends light exactly around the curvature of the earth, but I've seen books and papers that did the refraction math and ruled it out. I also saw a 20+ mile laser experiment, where they calculated the temperature/humidity differences all along the route of the laser and did the math, again ruling it out.
I was skeptical at first myself, but the more I dug and the more I dug, the more that the start realization hit me about how much we've been lied to, about everything.